The process involves three steps and uses two experiments.
First, run acquire a proton spectra with standard parameter Second, move the proton spectra to another experiment setup an array to determine the optimum decoupling power required. Third, apply the decoupling power to three areas of the spectra. One area where no peaks are present, then to the triplet, and then the quartet of ethyl benzene. The same procedure is applied to other molecules for their multiplets.
The procedure must be modified for applications other than the ethyl benzene example. Other VNMR experiments can be used instead of 1 and 2, i. e. move the spectra from 1 to 3, etc. mf(1,3) or mf(3,1)
1. Select experiment 1 and the standard parameters for 1H in CDCl3, set nt=1. Determine if the gain = Not Used, with the command gain? When the acquisition is complete display the spectra, scale and reference the center peak of the triplet to 1.24 ppm. Use the following commands: f full aph dscale nl rl(1.24p) Expand the scale around the triplet and reference the center peak f Display full spectra 2. Move the homodecoupling experiment to exp2 or any other which has been created as follows: jexp2 Join experiment 2 mf(1,2) Move fid with parameters from exp1 to exp2 wft Must transform the spectra at this point 2A. Set Homodecoupling Parameters homo='y' Select homonuclear decoupling mode dm='nny' Set decoupler to "on" only during acquisition gain='y' Turn off autogain gain? Shows gain value from prior acquisition 2B. Determine Optimum Decoupling Power(dpwr)
First expand around the triplet, then place the cursor at the center of the signal dscale Display the scale nl Select nearest line sd Set decoupler offset frequency (dof) for the triplet nt=4 Increase number of transients dpwr=24,26,28,30 Set up an array for dpwr (perhaps begin at 18) da Display the array and double check the settings ga Begin acquisition, will display each spectra sequentially When acquisition is complete, ds(1) Display first spectrum in the array (dpwr=24) Expand around the quartet and enter ai Select absolute intensity mode vsadj Adjust vertical scale vs=vs/2 Set vertical scale to half the current value. dssh Stack display of spectra horizontally Note: the optimum decoupling power is the minimum dpwr that achieves complete decoupling of the triplet. Complete decoupling of the triplet results in a collapsing of the quartet to a singlet. Record the optimum value for dpwr and apply in the final test. 3. Setup the Homodecoupling Experiment (Repeat the above protocol with the selected power.) 3A. Begin by again moving the spectra acquired in experiment 1, setting the dpwr and selecting three areas to decouple. The first area is away from any peak, the second at the center of the quartet, and the third area at center of the triplet. mf(1,2) Move fid with parameters from exp1 to exp2 wft Transform the spectra now 3B. Set the decoupling parameters dpwr=?? Set the decoupling power to a value 20? homo='y' Select homonuclear decoupling mode dm='nny' Set decoupler to "on" during acquisition, i. e. without NOE gain='y' Turn off autogain 3C. Set dof for the quartet and put it in to an array Expand around the quartet, set the cursor at the center of the signal and type sda Set decoupler offset frequency at the center of the quartet 3D. Set dof for the triplet and put it in to an array Expand around the triplet, set the cursor at the center of the signal and type nl Select nearest line sda Set decoupler offset frequency at the triplet put in the array da Display the dof array (about -425, -1365, and -1930 Hz) 3E. Start the Experiment dg Display group parameters nt=4 Increase number of transients ga Sequentially acquire array 3F. Phase and set the Display for an Arrayed Spectra ds(1) Display Spectrum 1 (control spectrum with no decoupling) f full aph Display full spectrum to full screen and autophase wp=2p Set width of plot in ppm sp=1p Set start of plot in ppm vsadj Adjust vertical scale vs=vs/4 Set vertical scale to 1/4 of the current value dssa Stack array of spectra vertically svf Save spectra after selecting your data file. 3G. Print the array text(`1H_Homodecoupling EtBz') Add requisite text to be printed with the spectra pl(1,3) pscale page Print stacked plot as displayed with scale 3H. Print parameter groups printon da dg dg1 dgs printoff Print parameter groups with the dof array list
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